The advantages and disadvantages of the high plateau known as Tibet are identical. The place is extremely hard to reach, hemmed in on the south by the Himalayas and on the north by the almost equally high Kunlun mountains. The terrain is inhospitable, the plateau itself being about 15,000 feet above sea level. The climate is harsh, with violent swings of temperature between night and day at all times of the year.

The disadvantage is that few people can live here. The advantage is that few others want to. Until modern times it has been impossible for outsiders to arrive in sufficient force to subdue the inhabitants for long.

Buddhist Tibet: 7th - 8th century

The story of Tibet moves in the 7th centuryfrom colourful legend into the realm of history. The change is the result of two new arrivals - writing and Buddhism.

As with the earlier example of Ulfilas and Gothic, the writing down of the Tibetan language appears to have been the work of one man. In about640 the king of Tibet sends a minister, Thon-mi Sambhota, to study Sanskrit in Kashmir. On his return he devises a new syllabary of 30 consonants and 4 vowels to suit his own entirely different Tibetan language (part of the Sino-Tibetan languages rather than the Indo-European family). Thon-mi Sambhota even finds time to write eight treatises on Tibetan grammar, two of which survive.

The same king of Tibet (Srong-btsan sgam-po by name) has two wives from alliances with neighbouring powers. One comes from Nepal, the other from China; both are Buddhist and both bring with them precious Buddhist images.

The king builds temples in his capital, Lhasa, to house his wives' sacred treasures. This is the first visible foothold of Buddhism in Tibet. Early in the next century the Indian religion receives a further boost when Buddhists from central Asia flee to this remote region to escape the advance of the Muslims. But it is not until the second half of the 8th century that Tibetan kings actively promote Buddhism as their state cult.

Tibet and China: 7th - 13th century

In the 7th and 8th centuries, under Srong-btsan sgam-po and his successors, Tibet is a unified kingdom exercising power over an area well beyond the Tibetan plateau, including important regions on the Silk Road such as Kashgar and Khotan. In 763 a Tibetan army even invades T'ang China and briefly captures the capital at Xi'an.

In subsequent centuries Tibet is more often a collection of small independent kingdoms, restricted to their own high plateau. They regard their large neighbour to the east with wary suspicion. A brief exception occurs in the 13th century, when a Tibetan link with the Mongol emperors of China brings Tibet formally within the Chinese empire.

In the early 13th century, when it is evident that Genghis Khan and his Mongol hordes represent a threat to China, the Tibetans make a successful attempt to befriend him. They pay tribute to the Mongols, and Tibetan Buddhist monks acquire influence at the Mongol court. By the middle of the century the abbot of a Buddhist monastery is ruling in Tibet as the viceroy of the Mongol khan.

On the replacement of the Mongol dynasty in China by the Ming, in 1368, Tibet reasserts its formal independence and retains it for the next three centuries.

Dalai Lamas: from the 14th century

From the 8th century various Buddhist monasteries in Tibet acquire strongly defined identities and become in effect separate sects within Tibetan Buddhism. Their abbots are men of power and importance.

In the 14th century the abbot of one such monastery declares that his reincarnated future self must be found and made abbot in his turn. The abbot dies in 1338. A child, born in 1340, is judged to be his reincarnation and is brought up to be head of the sect. These first two spiritual leaders, in a sequence still continuing, are later given the retrospective title of Dalai Lama. They are believed to have been incarnations of a Bodhisattva.

The third reincarnated abbot is the first to be called Dalai Lama in his lifetime. He is given the title by an admiring khan of one of the Mongol tribes. Dalai, relating to a Mongol word meaning 'ocean', is chosen to suggest the breadth and depth of the Lama's wisdom. Lama is the Tibetan word for 'superior', applied to a priest or a monk.

Perhaps not surpisingly, in view of this close link with the powerful Mongols, the fourth Dalai Lama is discovered in the person of a young Mongol prince. During his subsequent reincarnation, from 1617 to 1682 as the fifth Dalai Lama, there comes into being the form of government which until recent times has remained characteristic of Tibet.

Spiritual rulers of Tibet: 1642-1912

From about 1562 Tibet has been controlled by a self-made dynasty of kings, the Gtsang-pa. In 1642 a Mongol army removes them, and the khan presents the country to the Dalai Lama as a spiritual gift. The abbot is to rule it with Mongol military support.

In keeping with his new status, the fifth Dalai Lama moves his official residence to Lhasa and begins the construction of a palace - the Potala - on the site of the castle of the first historical king of Tibet, Srong-btsan sgam-po. The pattern of rule by the Dalai Lama, with military support from elsewhere (the Manchu dynasty in China later takes the Mongol role), lasts till the demise of the Chinese empire in the early 20th century.

Panchen Lamas: from the 17th century

The theme of appointment by reincarnation, introduced for the Dalai Lamas, is soon copied by many other Tibetan monasteries and sects. There are eventually several hundred who find their leaders in this way, but only one line of succession enjoys a prestige approaching that of the Dalai Lama. This is the line of the Panchen Lama (or more properly Pan-chen Rinpo-che, meaning 'Great Precious Sage').

The first Panchen Lama is the teacher of the fifth Dalai Lama. In about 1650 the grateful pupil declares (by means of a fortunately discovered text, revealing the truth) that his teacher is, like himself, an incarnation of a known Bodhisattva or future Buddha.

At the start the Panchen Lamas are merely abbots of a particularly important monastery, but they gradually become provincial governors on behalf of the Dalai Lama. This position brings wealth and political prestige, until in later centuries they are often seen as rivals of the Dalai Lama.

For each of these two sacred roles, and for many others of less importance, a search is rigorously conducted after each death to find the reincarnated infant. The selected boy is removed from his family and taken into a Buddhist monastery to be trained for the new chapter in his ongoing story, while a regent (an inevitable feature of the Tibetan system) carries out interim duties.

Manchu protection: 1720-1911

In the early 18th century warfare breaks out between two Mongol dynasties, competing to control Tibet through protection of the Dalai Lama. One side appeals to the Manchu emperor in Beijing for assistance. As a result Chinese imperial forces reach Lhasa in 1720.

For the rest of the Manchu dynasty, until 1911, the Chinese take on the role previously undertaken by the Mongols - that of providing force to protect the Dalai Lama or to restore order when needed, but otherwise leaving Tibet to its own devices.

The Chinese position is similar to that of a feudal overlord in medieval Europe - an ambiguous status which is used by Communist China in the late 20th century to provide historical justification for its occupation of Tibet.

The ambiguity exists much earlier. From 1861, when British India absorbs Sikkim, there are border and trade disputes with Tibet. By 1893 Britain believes it has resolved the issue in an agreement with Beijing. However the settlement is rejected by the Tibetans, who refuse to enter any form of negotiation with the British.

The result is an armed invasion from Sikkim in 1903 by a British force under Francis Younghusband. In August 1904, after frequently pausing en route in the hope of negotiation, the British enter the holy city of Lhasa. A treaty is agreed during the next month and is signed, amid great pomp, in the Potala. The terms, greatly advantageous to Britain, even allow for a measure of British control over Tibetan internal affairs.

The Manchu government, amending the treaty, prevents any British control over Tibet. But the Manchu link itself is now to prove short-lived. The revolution which topples the Manchus in 1911 in China also prompts the Tibetans to expel Chinese troops from Lhasa.